LVM driver not enforcing new size when creating share from snapshot

Description
===========
The kubernetes project "cloud-provider-openstack" has a devstack-based test job [1] to perform "e2e" tests. The devstack set up by the job uses the LVM driver [2]. A test case that seeks to "restore" a snapshot into a manila share of a larger size fails in this set up [3]. This is known to work as expected with other backends, since it is a generic expectation in manila as well. We may have an issue with the LVM setup that needs investigation.

We could further add a tempest test that creates a share of size X, writes data to it, snapshots it and creates a new share of size X+Y with the snapshot. We'd check in the test if the share is sized X+Y as requested.

Steps to reproduce
==================

A chronological list of steps which will help reproduce the issue you hit:
* Setup manila with devstack and LVM driver:
* Create a share of size 1
* Mount share, write some data into it
* Snapshot the share
* Create a new share from the snapshot with size 2
* Mount new share, verify size

Expected result
===============
Manila (and the backend driver) enforce the new size as requested, rather than the size of the original snapshot when creating a share.

Actual result
=============
New size not enforced when using the LVM driver.

Environment
===========
1. Exact version of OpenStack Manila you are running: OpenStack Zed

2. Which storage backend did you use? LVM

Logs
==============

Test Failure log: https://paste.openstack.org/show/bp2jrFVA6Y3IJ2spDCji/
df o/p with some instrumentation in the test: https://paste.openstack.org/show/bZi4IYxy6IXNSWVRZTci/

[1] https://prow.k8s.io/job-history/gs/kubernetes-jenkins/pr-logs/directory/openstack-cloud-csi-manila-e2e-test
[2] https://github.com/kubernetes/cloud-provider-openstack/blob/37a490ed46cea55d9d0d18230e78a19707142e05/tests/playbooks/roles/install-devstack/templates/local.conf.j2#L100-L115
[3] https://github.com/kubernetes/kubernetes/blob/3d27dee047a87527735bf74cfcc6b8ff8875f66c/test/e2e/storage/testsuites/provisioning.go#L452-L535